1. Field of the Invention
The present invention relates to portable transceivers such as cellular type mobile radio telephones which are driven by a battery power source to transmit and receive data on a plurality of channels (a plurality of frequencies) in a radio broadcasting manner and which have a function of stabilizing a consumption current and more particularly, to a portable transceiver which can average the quantities of currents different with respect to used channels and thus can maintain substantially the same power consumption in the battery power source with respect to the different channels even when any of the channels is used.
2. Description of the Related Art
FIG. 6 schematically shows a block diagram of an arrangement of the final stage of a prior art portable radio transceiver. The radio transceiver of FIG. 6 includes a power amplifier 1, an isolator 2, and an antenna 3. In operation, a signal 100 generated as a transmission signal at the previous stage of the transceiver is amplified with respect to power at the power amplifier 1, sent via the isolator 2 to the transmitting antenna 3, and then radiated from the antenna 3 in the form of transmission waves (electromagnetic waves).
Meanwhile it is known that the impedance of the above isolator 2 varies depending on the frequency of its input signal. More specifically, the isolator 2 has such a characteristic that the higher the frequency of the input signal is the larger the capacity is, and conversely the lower the frequency of the input signal is the larger the inductance is. The consumption current of the power amplifier 1 varies with the impedance of a load connected thereto and when the load has a large capacitive impedance, the power amplifier 1 has a small output current and thus requires a small consumption current. Conversely, when the load has a small capacitive impedance or a large inductive impedance, the power amplifier 1 requires its relatively large output current and thus a large consumption current.
Accordingly, in the case where such a portable radio transceiver transmits signals having a plurality of frequencies through channel switching operation:
(a) when the transceiver transmits a signal having a relatively high frequency through corresponding selected one (frequency) of the channels, the isolator 2 connected to the power amplifier 1 as its load has a large capacitive impedance, whereby the consumption current of the power amplifier 1 is suppressed to a low level and therefore the power consumption of the battery power source in the portable radio transceiver can be reduced.
(b) When the radio transceiver transmits a signal having a relatively low frequency, the isolator 2 connected to the power amplifier 1 as its load has a small capacitive impedance or has a large inductive impedance, which results in that the consumption current of the power amplifier 1 becomes large and therefore the battery power source of the portable radio transceiver is quickly and much consumed.
In this way, the consumption current of the power amplifier 1 and thus the power consumption of the battery power source (e.g., Ni-Cd battery) varies depending on the selected channel.
For this reason, in such a portable radio transceiver, generally speaking, it is difficult in actual circumstances to prescribe a standard battery device in its specification. In addition, with respect to differences in the power consumption of the battery power source between the use channels, the power consumption of the battery power source when one of the channels having a higher frequency is selected can be maintained or sustained for a relatively long; whereas, when one of the channels having a lower frequency is frequently selected, the power of the battery power source can be consumed unexpectedly quickly, thus causing an undesirable communication failure and a user to be confused.